HONG KONG – Hong Kong customs officers have made the territory's second largest ever drugs haul, seizing cocaine worth HK$260 million ($33.4 million) hidden in planks bound for mainland China. The seizure of 290 kilogrammes (639 pounds) of the drug was the largest yet made by the city's Customs and Excise Department and is believed to be the second biggest the city has seen, a customs spokesman told AFP Thursday. Customs officials discovered the drugs hidden in dozens of hollowed-out wooden planks in a shipment originating from Bolivia on December 29 last year, a statement on Wednesday evening said. Inside each of the planks were three slabs of cocaine wrapped in plastic and carbon paper, each weighing about 1.1 kilogrammes (2.4 pounds). The discovery was only made public Wednesday because officials were hoping that someone would claim the consignment, local reports said Thursday. The concealment method was "sophisticated" and "well thought out", the customs spokesman said. Carbon paper was used to try to avoid detection by X-ray machines, while plastic wrap and glue were used to mask the smell of the drug from sniffer dogs, he added. The shipment was trucked from Bolivia to Chile, where it was loaded onto a container ship. It arrived in Hong Kong via Taiwan late last month, where the city's customs officers discovered the cocaine. No arrests have been made so far. In April last year, Hong Kong police seized 372 kilogrammes (820 pounds) of cocaine with an estimated street value of $43 million in a village in northern Hong Kong while searching for a missing person. Figures show an upward trend in narcotics entering the former British colony through seaports rather than its airport, the spokesman said, adding that this has prompted customs officers to step up inspection of inbound shipments. "Customs will make every effort to ensure Hong Kong will not become a distribution point for drugs," he added. Under Hong Kong law, drug trafficking carries a maximum sentence of life imprisonment and a fine of HK $5 million ($643,000).